This invention deals generally with food processing and more specifically with apparatus for the freezing of ice cream and other products.
The typical commercial production of ice cream includes a piece of machinery which is quite impressive to those not in the ice cream processing business. The actual process of freezing the ice cream and similar products involves the use of a machine the smallest of which is approximately 15 feet high, 20 feet wide and 30 or more feet long. This entire machine is enclosed in a room which is held at a subfreezing temperature, cold enough to freeze ice cream or other frozen products, and containers filled with soft ice cream are loaded into and moved continuously though the machine so that they are frozen hard when they are later discharged from the machine.
The essential moving elements of the machine are large, multiple shelf racks, called transports in the industry, onto which many containers are loaded and which then progress through the machine as subsequent similar transports are loaded and move behind. Each of these freezer transports is typically 15 feet long, 1 to 2 feet deep, 5 to 14 feet tall, and has 4 to 14 shelves. When such a transport is fully loaded with, for example, half gallons of ice cream, its total weight can be as much as 2000 pounds. Nevertheless, the whole transport is moved through the machine, and in a low temperature environment which subjects machinery to significant problems.
The transports are constructed with a set of two wheels outriggered on each of the narrow sides. The wheels are located above the center of gravity of the transport. These wheels engage a track running along the long side of the machine so that the basic path of motion of the transports is from one end of the machine to the other. As each transport reaches the end of the machine an elevator within the machine picks it up and lifts it above the following transports which fill the entire path through which the transport has just moved.
Each transport is then moved in sequence in the opposite direction and above the initial path until it reaches the end of the machine from which it originally started. The upper return movement takes place with the transport's wheels engaging the same type of track as is built onto the lower path. At the entry end of the machine each transport is individually moved onto another elevator which lowers it to the lower level. It is during the lowering of the transports that the loading and unloading occurs using loading and discharge conveyors which pass through the machine in the region of the machine between the upper and lower levels of the moving transports.
The loading and unloading takes place as a transport is lowered in steps equal to the spacing between the shelves on the transports. As the lowest shelf moves to and stops at the level of the discharge conveyor, an unloading arm which is essentially the same size as the length of the shelf moves over the shelf from front to back and pushes all the containers with frozen product from the shelf onto the discharge conveyor which is located immediately behind the shelf. After the unloading arm retracts, the transport is then moved down the distance of one shelf height, and a loading arm, which is synchronized with the unloading arm, pushes new containers with soft product from the loading conveyor in front of the shelf onto the shelf. At the same time the lowest shelf is being loaded, the unloading arm is unloading the next higher shelf. This simultaneous loading and unloading of the shelves continues until the entire transport is loaded with new, soft, product, and the transport then again begins its travel through the machine.
As can be appreciated from the above description of the machine's operation, it is always essentially full of product, and even the smallest of such machines have 24 transports with 4 shelves and hold a total of approximately 10,000 half gallon containers. Under such conditions it is quite clear that a breakdown on such a machine presents very difficult problems. Particularly, a breakdown of such a machine which is caused by a transport jamming and not moving forward can mean the need to manually unload a substantial part of the product from the machine, and to do so in a subfreezing environment, just to get at the jammed transport. Yet, such breakdowns are not uncommon.
The major reason for the failure of a transport to move as it is pulled along by chains is the failure of one of the wheel bearings. Furthermore, with a total of approximately 100 wheels on all the transports in even a small machine, it appears that statistically one of those wheels will always be due for a failure. This is certainly true when the subfreezing environment of operation is considered, since such conditions are so detrimental to the wheel lubrication, and particularly when, for purposes of energy conservation, the transports are kept at the subfreezing temperatures and operated continuously until a wheel bearing fails.